fix: add required connection retry configs to E2E tests

Add missing connection retry configuration parameters:
- connection_retry_attempts: 3
- connection_retry_backoff: 0.5
- connection_retry_backoff_max: 5.0
- pool_close_timeout: 5.0

These are required by PostgreSQLDB initialization.

Issue: KeyError: 'connection_retry_attempts' in E2E tests

tests/test_e2e_postgres_migration.py

@@ -31,6 +31,11 @@ def pg_config():
         "database": os.getenv("POSTGRES_DB", "lightrag_test"),
         "workspace": os.getenv("POSTGRES_WORKSPACE", "e2e_test"),
         "max_connections": 10,
+        # Connection retry configuration
+        "connection_retry_attempts": 3,
+        "connection_retry_backoff": 0.5,
+        "connection_retry_backoff_max": 5.0,
+        "pool_close_timeout": 5.0,
     }